The present invention relates to a channel-selecting apparatus for a multichannel transceiver, and more particularly to improvements on a channel-selecting apparatus for a multichannel transceiver which is designed to select any desired channel by changing transmission-reception signal frequencies specified for the respective channels utilizing a phase locked loop system.
The prior art practical channel-selecting apparatus for a mutlichannel transceiver is generally provided with a multipole-multiposition type rotary changeover switch and is so designed that a specified code signal representing any selected channel number is generated upon operation of said changeover switch and said specified code signal is conducted to a programmable counter included in the phase locked loop so as to decide the ratio in which said counter divides its input signal frequency, thereby picking up any desired channel. However, the prior art channel-selecting apparatus of the above-mentioned mechanism has the following drawbacks. Namely, the specified code signal generally consists of a binary coded decimal signal. Since, in this case, a 4-pole-10-position type rotary changeover switch is required to denote any decimal numeral of the first place, the larger the number of channels being selected, not only the more complicated the mechanism of an assembly of said rotary changeover switches, but also the larger the space occupied by the switch assembly.
Further as is well known to those skilled in the art, when the ratio in which a signal frequency is divided by the programmable counter is changed in turn by the successive operation of said rotary changeover switch, then the frequencies of local oscillation signals generated for the respective channels by the phase locked loop are successively shifted at an equal frequency interval on the basis of a unit frequency interval defined by a signal frequency given forth by the later described fundamental signal oscillator included in the phase locked loop. Where, therefore, transmission-reception signal frequencies specified for the respective channels and in consequence local oscillation signal frequencies for said channels are all arranged at an equal frequency interval, there is not raised any problem in selecting a desired channel. According to the frequency assignment adopted for the American 23-channel citizen band transceiver, however, transmission-reception signal frequencies f.sub.t specified for the respective channels and in consequence local oscillation signal frequencies f.sub.0 for said channels are not arranged at an equal frequency interval (namely, different frequency intervals of 10 kHz, 20 kHz and 30 kHz appear in some places of both frequency arrangements) as shown in Table 1 below.
Table 1 ______________________________________ Channel f.sub.t (MHz) f.sub.0 (MHz) ______________________________________ 1 26.965 38.240 2 26.975 38.250 3 26.985 38.260 4 27.005 38.280 5 27.015 38.290 6 27.025 38.300 7 27.035 38.310 8 27.055 38.330 9 27.065 38.340 10 27.075 38.350 11 27.085 38.360 12 27.105 28.280 13 27.115 38.390 14 27.125 38.400 15 27.135 38.410 16 27.155 38.430 17 27.165 38.440 18 27.175 38.450 19 27.185 38.460 20 27.205 38.480 21 27.215 38.490 22 27.225 38.500 23 27.255 38.530 ______________________________________
Moreover, said 23 channels are numbered in increasing order, starting with those having smaller allotted frequencies. Where it is a legal obligation to indicate these channel numbers, then the undermentioned difficulties arise. Above all, the ratios of frequency division by the programmable counter which are specified for the respective channels are not in consecutive order. Namely, some exceptional frequency division ratios can not be used in channel selection. As the result, coincidence does not take place between the channel numbers displayed by the successive operation of the rotary changeover switch and an advance in the ratios of frequency division by the programmable counter, thus making it practically impossible to select any of the channels whose numbers are indicated by decimal numerals of two or more places by applying the above-mentioned type rotary changeover switch to the numerals of each place.
It is accordingly the object of this invention to provide a channel-selecting apparatus for a multichannel transceiver, the channel-selecting switch assembly of which is far more simplified than in the prior art channel-selecting apparatus regardless of the number of channels being selected and which is readily applicable even when transmission-reception signal frequencies specified for the respective channels are not arranged at an equal frequency interval.